POS to QB inventory posting problem

Client does warranty work where the warranty company pays for a portion (usually parts only) k & customer pays balance (usually labor).  For warranty work only, POS will not transfer reduction in inventory for parts used to QB UNLESS warranty/customer sales are separate in POS.

Had been creating one sale and receiving payment from 2 sources but this results in QB not getting an inventory reduction.  Inventory reports in POS are off as well.